Converting a 4:3 VOB with Avidemux (it's giving me 3:2)

[pooksahib]

A DVD I'm trying to copy has VOBs of 720x480, NTSC 4:3. I've found that using x264 at 1500fps with either Avidemux or Hybrid gives excellent results. However, while the latter generates a 4:3 picture, Avidemux gives me 3:2 which is a wider image on my TV (although the distortion is barely noticeable).

In the 'Output 1' tab of Avidemux are 3 radio buttons:
'Predefined Aspect Ratio'. Selecting 4:3 here still generates 3:2.
'As Input'. This sounds like what I need but is greyed out.
'Custom'. The default is '1' and '1' but I don't fully understand this setting.

Can anyone tell me how to get a 4:3 file from Avidemux? I know I could just use Hybrid but it blurs the first few frames of each VOB.

My thanks in advance.

[LigH.de]

Content on a DVD is always anamorphic. Always. No matter which encoded resolution is stored (there are several allowed), the displayed aspect ratio of either 4:3 or 16:9 has to be achieved by deskewing the image.

Encoding a copy of the video, you can either keep the original resolution and have an aspect ratio flag stored so that the player will deskew the anamorphic image to the desired display aspect ratio; but that requires that the encoding application is able to put the correct flag into the destination video stream or container (possibly both), and the player can interpret such a flag and scale the video while playing.

Or you may prefer to deskew the image while converting, so that the copy will have a pixel (sample) aspect ratio of 1:1 (= needs no deskewing while playing). Unfortunately, Avidemux mixes DAR and SAR in the same list without denoting the difference; your desired settings will probably be:

Source: 4:3
Destination: 1:1

Width: 640
Height: 480

(it is useful to try to keep the height unchanged, especially because NTSC might have combing if you don't try to detect and possibly remove interlacing vs. telecine)


By the way:

1500 "frames pro second" (a speed) is probably not what you mean, rather 1500 "kilobits per second" (a bitrate). But in general, I would not recommend to rely on a bitrate, because every movie may have a different complexity and may need a different minimum bitrate to look acceptable.

[pooksahib]

Hi LigH.de and thank you very much for that. You're right, my '1500fps' was a lapse of concentration. I always convert using 2-pass average bitrate as opposed to fixed and 'average 1500' usually gives good results.

I tried Avidemux again but the Filter/Resize option won't allow 640x480 – when I input 640, the opposite number changes to 426...

Not to worry, I discovered how to make Hybrid accept all 5 VOBs in one go and it's done a fine conversion job for me.

Thanks again for your time.

[LigH.de]

I tried Avidemux again but the Filter/Resize option won't allow 640x480 – when I input 640, the opposite number changes to 426...

Did you set AR { Source: 4:3 | Destination: 1:1 } before changing to 640 pixels width?

[DB83]

640*426 implies that your source or even destination is actually 16:9 and not 4:3

[pooksahib]

Hi again. Yes, I left the '640' setting to last but it just won't go to 640x480. But never mind – what DB83 said made me carry out a little experiment...

You see, mediainfo told me that the VOBs were 4:3 and I assumed that to be fact. However, by playing a VOB in PotPlayer (an excellent player, by the way) I've discovered that the VOB picture really is 3:2. Setting the AR in PotPlayer to 'source' and then switching it to '3:2' gives an identical picture which the eye can see is correct. Setting PotPlayer to 4:3 or 16:9 gives a 'wrong' picture.

So I've learned that it's better to trust PotPlayer than my telly...

And I can now stick with Avidemux. Thanks again, guys.

[poisondeathray]

Hi again. Yes, I left the '640' setting to last but it just won't go to 640x480. But never mind – what DB83 said made me carry out a little experiment...

You see, mediainfo told me that the VOBs were 4:3 and I assumed that to be fact. However, by playing a VOB in PotPlayer (an excellent player, by the way) I've discovered that the VOB picture really is 3:2. Setting the AR in PotPlayer to 'source' and then switching it to '3:2' gives an identical picture which the eye can see is correct. Setting PotPlayer to 4:3 or 16:9 gives a 'wrong' picture.

So I've learned that it's better to trust PotPlayer than my telly...

And I can now stick with Avidemux. Thanks again, guys.

Is this a retail DVD? Because no VOB from a retail DVD will be 3:2. DVD-Video only supports 4:3, 16:9. 3:2 would imply square pixels for NTSC 720x480 (because 720/480 = 1.5 or 3/2)

Now there are might be some bizarre DVD recorders that record 3:2, or sometimes the software player gets fooled because there is extra information in the sequence display extension

[pooksahib]

Hi poisondeathray. A normal DVD...
As I said, when switching PotPlayer's AR setting between 'source' and 3:2, the frame size doesn't change which suggests the movie IS 3:2. But, having looked again, both 3:2 and 4:3 (in PotPlayer) are pleasing to the eye - I just can't decide which is 'right'.

But then I had an idea - play the VOB on the TV. It plays 4:3. As a result I'll use the file generated by Hybrid.

[manono]

As I said, when switching PotPlayer's AR setting between 'source' and 3:2, the frame size doesn't change which suggests the movie IS 3:2.

Impossible. I've seen this exactly once in my life, where the 720x480 picture had the 'normal' appearance but when playing the DVD at 4:3 it 'looked' wrong. It was a crap Indian DVD of the 1951 film Bahar and the Indian encoders were complete fools, even more than usual.

Do you have a short 10 second sample?

[pooksahib]

Hi manono. After reading your post, I had another brainwave – PotPlayer has a 'File Info' feature for whatever it's currently playing. Here's what it says:
Video
ID : 224 (0xE0)
Format : MPEG Video
Format version : Version 2
Format profile : Main@Main
Format settings, BVOP : No
Format settings, Matrix : Custom
Format settings, GOP : M=3, N=15
Duration : 30mn 49s
Bit rate mode : Variable
Bit rate : 4 360 Kbps
Maximum bit rate : 7 341 Kbps
Width : 720 pixels
Height : 480 pixels
Display aspect ratio : 4:3
Frame rate : 29.970 fps
Standard : NTSC
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan order : Top Field First
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.421
Time code of first frame : 00:00:00:00
Time code source : Group of pictures header
Stream size : 961 MiB (94%)

As I mentioned in post #6, mediainfo also puts the AR at 4:3 so we can safely say that's what it is. Maybe I don't fully undertstand the settings of PotPlayer. 'AR-Source' is the same as 'AR-3:2' - my assumption was that 'Source' means the true AR of the input file. Maybe that's not the case...

If I set PotPlayer to 'Display AR (recommended)' I get the same framesize as 4:3.

I've got a fine conversion with Hybrid so I declare the matter closed. My grateful thanks to you all.

[DB83]

Can you give the same detailed report for your conversion as it plays. There, in my eyes, are still some anomalies.

[pooksahib]

Hi DB83. As requested, here's what PotPlayer has to say about the file I created with Hybrid:

Format : MPEG-4
Format profile : JVT
Codec ID : avc1
Writing application : Hybrid 2014.06.17.2
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Bit rate : 1 500 Kbps
Maximum bit rate : 2 661 Kbps
Width : 720 pixels
Height : 480 pixels
Display aspect ratio : 4:3
Original display aspect ratio : 4:3
Frame rate mode : Constant
Frame rate : 29.970 fps
Standard : NTSC
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.145
Stream size : 1.44 GiB (88%)
Writing library : x264 core 142 r2 a5831aa

[DB83]

Well that seems ok. Was somewhat thrown when you said that one program wanted to create 640*426.

Out of interest, since we have not seen a sample of the video, do you see any black bars on the top and bottom of the picture ?

[pooksahib]

It's barless. I think it's just Avidemux that has the trouble (the file it created was 3:2). Interestingly, I've just loaded a VOB into Avidemux and clicked on 'File/Information' (I hadn't noticed that before) and the AR is shown as "NTSC 4:3 (8:9)". What's the 8:9 about??

Anyway, my original question was How do I get Avidemux to generate a 4:3 conversion file using the x264 codec. Despite having “Configure/Output1/Predefined Aspect Ratio” set to 4:3, I was getting 3:2. In post #2 it was suggested I set the dimensions to 640x480 but I said I couldn't as setting 640 made the other figure change to 426. I've discovered why that happened – there's a tickbox in the 'Resize' tab called 'Lock Aspect Ratio' which I hadn't unticked. Now that I have, I can specify 640x480 and the resulting file is 4:3. Which is nice...

However, I'm sticking with Hybrid as it gives the correct output without having to instruct a resize.

Once again, my thanks to all.

[DB83]

the 8:9 is the pixel aspect ratio(PAR). For pal 4:3 you would see 16:15. dvd pixels are non-square whereas your converted video could have square pixels(1:1) and some codecs allow for non-square.

What that means is that the width is shortened so 720*480 is properly displayed as 640*480 whereas with PAL the width is stretched so 720*576 becomes 768*576.

[LigH.de]

People still get confused between

a) the aspect ratio the image is encoded to (has no meaning; the 3:2 of 720:480 is irrelevant for "Generic AR" of MPEG2 video in DVD — in theory...)
b) the aspect ratio the image should be displayed with, after deskewing (in ISO/IEC 13818: "Display Aspect Ratio"= DAR; typical: 4:3 or 16:9)
c) the factor the image has to be deskewed by to obtain the DAR (in ISO/IEC 13818: "Sample Aspect Ratio" = SAR, elsewhere a.k.a. PAR); the image is "anamorphic" if it is not 1:1

ISO/IEC 13818 is the "core" of the MPEG2 specification (container, video, and audio formats), Part 2 (video) is related to ITU-T Rec. H.262.

Video on a "DVD Video" disc is always anamorphic, there is never a "square pixel" format.

MPEG2 video only defines 4 valid aspect ratios: SAR 1:1 (not allowed on DVD), DAR 4:3, DAR 16:9, or DAR 2.35:1 (not allowed on DVD). No matter if you have PAL (576 lines) or NTSC (480 lines), and if you have a width of 352, 704, or 720 pixels ... the encoded image always has to be resized until the displayed image has an aspect ratio of either 4:3 or 16:9, if your source was a "DVD Video" media.

Unfortunately, some producers incorrectly scale digitized TV signals for DVDs. They have a different rule set of aspect ratios, based on milli and micro second timings (if you had captured analogue video signals, this would be relevant as deskewing factor, see c) above). And analog video signal generators in DVD players are not reliable either if they create a video line timing for the whole encoded width or take the outer areas as overscan ... that's a discussion of a whole previous decade. Please don't continue that here.

[DB83]

'Sample Aspect Ratio' where did that expression come from ?.

SAR = 'Storage Aspect Ratio' which is precisely what 720*480 or 720*576 are.

[jagabo]

'Sample Aspect Ratio' where did that expression come from ?.

AVC spec.

My guess is some engineer decided to be pedantic and correct the mistake: pixel are points, they have no aspect ratio. What people had been calling pixel aspect ratio was really the spacing between the pixels, the sampling aspect ratio.

[DB83]

DOH !

Well I will be pedantic now

We are (or were) referring to dvds which are not part of the AVC spec.

[LigH.de]

'Sample Aspect Ratio' where did that expression come from ?.

I remember that I wrote: ISO/IEC 13818-2.

But yes, there are always different possible interpretations of single characters. S may be "Sample" or "Storage". P may be "Pixel" or "Picture". This interpretation may vary from one specification to another (e.g. from MPEG2 to MPEG4).